Re: Gandalf's mark
Well, I don't know anything about Germanic or any runes, but if your interpretation is correct we have the solution, Alcuin:
B - Burglar
D - Danger/Excitement
Diamond shape (point or not) - Reward
It sounds logic too that Tolkien would have used "real" runes for that kind of inscription, after all his "LotR" runes are based on these and he was what we would call fluent in them.
So live for every moment as the world keeps turning round, And lift your hands up to the sky and say it loud and proud, "I have been here"
Chris de Burgh